Magnetic core forming apparatus

ABSTRACT

Apparatus for forming toroidal magnetic cores by compressing powdered ferrite material, including a punch for compressing the material and a stationary core rod extending through the punch to form the hole of the toroidal core, wherein the punch and core rod are constructed to reduce breakage of the core rod. The punch has a hole with a narrow forward end and a wide rearward end, and the core rod has a narrow forward end that slide through the forward end of the punch hole and a wide rearward portion for moving along the rearward end of the punch hole. The rearward portion of the core rod is sufficiently smaller than the rearward end of the punch hole to prevent sliding contact with the walls of the punch hole thereof, to eliminate friction therealong as the punch reciprocates. Yet, the diameter of the rearward core rod portion is much larger than the forward core rod portion, to reduce the unsupported length of the forward core rod portion where breakage is likely to occur.

United States Patent 1191 Bryant MAGNETIC CORE FORMING APPARATUS [75] Inventor: Jack R. Bryant, Freehold Township,

[73] Assignee: Electronic Memories and Magnetics Corporation, Los Angeles, Calif.

[22] Filed: Dec. 17, 1970 [21] Appl. N0.: 99,079

Primary ExaminerRobert L. Spicer, Jr. AttorneyLindenberg, Freilich 5: Wasserman I, mmv

l IIIA IIIIIIIIIIIIIA 1 1 Apr. 17, 1973 [5 7] ABSTRACT Apparatus for forming toroidal magnetic cores by compressing powdered ferrite material, including a punch for compressing the material and a stationary core rod extending through the punch to form the hole of the toroidal core, wherein the punch and core rod are constructed to reduce breakage of the core rod. The punch has a hole with a narrow forward end and a wide rearward end, and the core rod has a narrow forward end that slide through the forward end of the punch hole and a wide rearward portion for moving along the rearward end of the punch hole. The rearward portion of the core rod is sufficiently smaller than the rearward end of the punch hole to prevent sliding contact with the walls of the punch hole thereof, to eliminate friction therealong as the punch reciprocates. Yet, the diameter of the rearward core rod portion is much larger than the forward core rod portion, to reduce the unsupported lengthof the forward core rod portion where breakage is likely to oc- 4 Claims, 5 Drawing Figures PATENTEDAPR 1 H973 4 \I'HCK R. 252 mdr I N VENTOR.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to apparatus for forming magnetic cores by compressing powdered material, and more particularly, to apparatus for forming substantially toroidal magnetic cores.

2. Description of the Prior Art One method of forming magnetic cores includes pouring powdered magnetic material into a die, holding an anvil at one end of the die and moving a punch along the die towards the anvil to compress the magnetic material. In order to form a toroidally shapedcore, the punch is provided with a small central hole and a thin core rod extends through the die cavity and the punch hole. The core rod is made of a hard material such as tungsten carbide, which is also very brittle. The fact that the core rod has a long thin region makes it highly subject to breakage, resulting in'increased costs due to down time of the machinery and the cost of replacing the core rod. A construction of a core rod which resulted in substantially less breakage would greatly increase the production obtainable from core forming machines while reducing the cost of replacing core rods.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide tools for forming magnetic cores, which are more resistant to breakage than tools previously available.

Another object is to provide tools for forming magnetic cores which create less heat and wear.

In accordance with one embodiment of the present invention, machinery is provided for compressing powdered magnetic material into the shape of toroidal cores, which includes a punch and core rod that resist breakage. The punch, which moves in a forward direction along a die to compress powder, has a central hole through which the core rod slides, this hole having a small diameter forward portion and a larger diameter rearward portion. The core rod which slides along the punch, has a narrow forward portion which is closely received in the forward punch hole portion, and an enlarged rearward portion that can move along the rearward punch hole portion.

The fact that the enlarged rearward core rod portion can be received in the punch hole means that it can support more of the thin forward end of the core rod, to minimize the likelihood of breakage. A long punch can still be used, since the enlarged rearward hole portion of the punch can accomodate the enlarged rearward core rod portion. The walls of the rearward hole portion have a much larger diameter than the rearward core rod portion, so there is generally no sliding con tact between them and therefore no frictional heat is created therealong. The large clearance between the rearward core rod portion and walls of the punch hole also allows large manufacturing tolerances therealong without causing breakage of the core rod.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional side view of core forming apparatus constructed in accordance with the present invention;

FIG. 2 is an enlarged view of a portion of the core forming apparatus of FIG. 1;

FIG. 3 is a view taken on the line 3-3 of FIG. 2;

FIG. 4 is a sectional side view of the core rod of FIG. 2; and

FIG. 5 is a sectional side view of the punch of FIG. 2.

DESCRIPTION THE PREFERRED EMBODIMENTS FIG. 1 illustrates apparatus for forming toroidal magnetic cores of a type which may be used in computer memories. As also shown in FIG. 2, the apparatus includes a die bushing or die 10, a punch 12 that moves through a hole in the die, and a core rod 14 that extends through a hole in the punch. The die 10 is held stationary in a die plate 16, and the core rod 14 is held stationary in a core rod holder 18. The punch 12, however, is mounted on a punch holder 20 that can reciprocate up, or forward, towards an anvil 22 and down, or rearwardly, away from it. A magnetic core is formed by pouring ferrite powder into a central hole 24 in the die 10, moving the anvil 22 over the die hole, and moving the punch 12in a forward direction towards the anvil to compress the powder into av toroidal shape around a forward end 26 of the core rod 14. After the core is thus formed the anvil 22 is removed, a vacuum head (not shown) is moved over the die 10 to pick up the formed core and move it to a collecting basket; and another measure of powder is inserted into the die hole. The toroidal cores thus formed may be sintered in an oven and used to form a computer memory. Typically, the core forming machine includes several dies 10 and a corresponding number of punches and core rods for forming several cores at a time.

The forward portions of the punch 12 and core rod 14 that contact the powdered magnetic material are subject to rapid wear, since the powdered material is highly abrasive. To maximize tool life, the punch 12 is constructed of a wear resistant material such as tung sten carbide, and the forward end 26 of the core rod is also constructed of such a material. Even these materials experience rapid wear, and the tips must be ground and lapped flat at intervals. The punch 12 must have a relatively long forward portion 30 of a diameter that can be received in the die hole 24, to allow for considerable movement during punch reciprocation in the die 10 and to provide an extra length for repeated resharpening. The core rod 14 requires a very long forward end 26 of constant small diameter, to project completely through the forward punch portion 30 and past it to the upper surface of the die 10, and also to provide an additional length for repeated sharpening. The core rod has a rearward shank portion 32 of increased diameter and a more ductile material than tungsten carbide. However, the forward end 26 which is of a constant small diameter is long in relation to its diameter.

One type of core rod that has been previously used, employed a forward end of constant small diameter which extended completely through the entire length of the punch 12, and for a distance in front of and behind the punch to allow for punch movement and to allow for changes in length due to sharpening. The fact that the rod had a long length portion of small diameter and of brittle material resulted in =a high frequency of breakage. In addition, the long length of contact between the core rod and the punch hole walls resulted in the generation of substantial amounts of heat, leading to even more breakage. Although the walls of the punch hole and the small diameter forward end of the core rod were highly finished, the fact that it was necessary to maintain extremely small clearances between them could result in binding and breakage if they were unevenly heated.

In accordance with the present invention, the punch 12 and core rod 14 are constructed to provide maximum support for the forward end 26 of the core rod and to minimize heating of it as the punch 12 slides forward and rearwardly. Referring to FIG. 4, it is seen that the core rod 14 includes a long pin 34 of constant outer diameter A and a shank 32 with a forward part 36 of a larger diameter B than the core rod and a rearward part 38 of a still larger diameter. While the pin 34 is constructed of a hard brittle material, the shank 32 is constructed of a more ductile material such as tool steel. The pin and shank are brazed together at the rearward end at 37.

The punch 12, which is best shown in HO. 5, is constructed of a single piece of tungsten carbide. A central hole 40 extends throughout the length of the punch, and includes a forward portion 42 of a diameter C approximately equal to the diameter A of the core pin 34, and a rearward portion 44 of a diameter D which is larger than the diameter B of the forward shank part 36. The punch has a middle portion 46 and rearward portion 48 which are held in the punch holder 20 that reciprocates the punch. Normally, the forward portion 30 of the punch must be at least a predetermined length in order to move along the die and to provide an extra length for sharpening, while the region behind the forward part 30 must also be of a substantial length in order to be easily held in the punch holder. The rearward punch hole portion 44 preferably extends along as much of the length of the punch as possible, to receive a long length of the core rod shank 32, so that the thin forward core rod portion 26 can be as short as possible. However, the hole 44 cannot extend too far or else it will weaken the punch. The use of the enlarged diameter punch hole portion 44 allows the shank part 36 to be received in the punch to minimize the unsupported length of the carbide pin without requiring any shortening of the punch. The reduced unsupported length of the carbide pin 34 reduces the amount of breakage. The unsupported length of the pin 34 (along the forward portion 28) is still large compared to its diameter, often being over twenty-five times as great. Similarly, the forward punch hole 42 generally has a length over five times its diameter, and often more than fifteen times as great.

The diameter A of the forward core rod portion 26 is nearly equal to the diameter C of the forward punch hole portion to provide only a very small clearance between them. For a typical forward core rod diameter A of 0.016 inch, a diametric difference CA may be specified which is less than 2/ 10,000 inch. The difference between the diameter B of the shank portion 36 and the diameter D of the punch hole portion 44 in which it is received is substantially greater than 2/ 10,000 inch, and preferably is greater than five times as much, or more than 1] 1000 inch. The greater clearance results in the shank portion 36 not contacting the walls of the hole 44 under normal usage. This lack of contact means that no frictional heating occurs along this region and therefore the amount of heating of the core rod is minimized to further reduce the possibility of breakage.

It is generally desirable to not allow too much clearance between the walls of hole 44 and the shank portion 36. By making the punch hole diameter D only moderately greater than the shank portion B, breakage is reduced during installation. For example, when a workman inserts the core rod and pushes sidewardly on it, the shank portion 36 will touch the walls of hole 44 after a small deflection to prevent a larger deflection that can break the forward core rod portion 26. During normal machine operation, however, sliding contact generally does not occur. It may be noted that the large clearance between the punch hole portion 44 and shank portion 36 allows for a greater deviation from true concentricity of the core rod portions 26 and 36 and of the shank hole portions 42 and 44 without affecting their performance. Tools have been constructed wherein the diameter A of the forward core rod portion was nominally 0.016 inch and the diameter B of the shank portion was nominally 0.04 inch. The maximum difference C-A was 0.00015 inch while the minimum difference D-B was specified to be 0.005 inch, or over 10 times as great.

Thus, the invention provides a punch and core rod which are constructed to allow a long punch to be used while minimizing the unsupported length of the brittle core pin material. This is achieved by providing an enlarged rearward punch hole portion and by providing a supporting shank on the core rod that can be received in the enlarged punch hole portion. Heating of the core rod and punch is minimized by making the rearward punch hole portion large enough to substantially eliminate contact with the shank portion therein during normal operation.

Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art and, consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

What is claimed is:

1. In an apparatus for forming magnetic cores including a die with a hole of a diameter equal to that of a core to be formed, an anvil movable over an end of the die, means for moving a punch with a hole therein forward along said die hole towards said anvil to compress powder in said die hole, and means for holding a core rod in stationary extension through said hole in said punch, the improvement comprising:

a punch having a hole extending therethrough with a forward end portion of a first diameter and a second portion behind said forward end portion of a second diameter greater than said first diameter; and

a core rod extending completely through said punch hole and having a forward end portion longer than said punch hole forward end portion and of substantially the same diameter to provide a close sliding fit therewith, said core rod also having an elongated second portion behind said forward core rod end portion of a diameter larger than said forward portion of the rod and smaller than said second portion of the punch hole;

the clearance between said second core rod portion and the walls of said second punch hole portion being at least five times greater than the clearance between said forward core rod end portion and the walls of said forward punch hole end portion, even as a proportion of the diameters of the core rod portions, whereby to substantially eliminate frictional heating along said second core rod portion.

2. Apparatus for pressing magnetic cores comprising:

a die having a central hole for receiving magnetic core material;

an anvil movable over said die;

a punch movable at least partially in a forward direction through said die to compress said material against said anvil, said punch having a central hole;

a core rod extending completely through said punch hole, and having a forward end of a first predetermined diameter for extending through said hole in said punch and up to said anvil to form the central hole in a core, and having an elongated second portion of a second predetermined diameter which is greater than said first diameter;

said hole in said punch having a forward portion of a diameter approximately equal to said first predetermined diameter of said forward core rod end to form a close sliding fit therewith, and said 'hole in said punch having a rearward portion which is of a diameter sufficiently greater than said second predetermined diameter of said second core rod portion to provide a clearance of at least five times the clearance around said forward core rod portion, to substantially prevent sliding contact between the punch and core rod therealong;

means for holding said core rod stationary with its extreme forward end approximately even with said anvil; and

means for reciprocating said punch toward and away from said anvil.

3. Apparatus for pressing magnetic cores comprising:

a die of hard material having a central hole for receiving magnetic core material;

an anvil movable over said die;

means for reciprocating a punch along said die;

means for holding a core rod in extension through a hole in a punch that is being reciprocated and in extension through said die up to said anvil;

a punch of hard material having a hole extending therethrough, said punch hole having a forward hole portion of a first diameter and a rearward hole portion of a second diameter greater than said first diameter, the outside of said punch having a forward part with a diameter approximately equal to the diameter of said die hole and a rearward part of a greater diameter; and

a core rod extending completely through said punch hole, and including a pin of hard material of a constant diameter substantially equal to said first diameter of said punch hole and an elongated support of a material less hard and less brittle than the material of said pin, said support having a central hole of a diameter approximately equal to the diameter of said pin and said pin extending through said support hole and fastened to said support, said support having a forward part of a diameter sufiiciently less than said second diameter of said punch hole to provide a clearance of at least five times the clearance around said forward core rod portion, to prevent contact with the walls of said punch hole in normal operation.

4. The apparatus described in claim 3 wherein:

the difference between said second diameter of said punch hole and said forward part of said support of said core rod is more than ten times as great as the difference between said first diameter of said punch hole and the diameter of said pin of said core rod. 

1. In an apparatus for forming magnetic cores including a die with a hole of a diameter equal to that of a core to be formed, an anvil movable over an end of the die, means for moving a punch with a hole therein forward along said die hole towards said anvil to compress powder in said die hole, and means for holding a core rod in stationary extension through said hole in said punch, the improvement comprising: a punch having a hole extending therethrough with a forward end portion of a first diameter and a second portion behind said forward end portion of a second diameter greater than said first diameter; and a core rod extending completely through said punch hole and having a forward end portion longer than said punch hole forward end portion and of substantially the same diameter to provide a close sliding fit therewith, said core rod also having an elongated second portion behind said forward core rod end portion of a diameter larger than said forward portion of the rod and smaller than said second portion of the punch hole; the clearance between said second core rod portion and the walls of said second punch hole portion being at least five times greater than the clearance between said forward core rod end portion and the walls of said forward punch hole end portion, even as a proportion of the diameters of the core rod portions, whereby to substantially eliminate frictional heating along said second core rod portion.
 2. Apparatus for pressing magnetic cores comprising: a die having a central hole for receiving magnetic core material; an anvil movable over said die; a punch movable at least partially in a forward direction through said die to compress said material against said anvil, said punch having a central hole; a core rod extending completely through said punch hole, and having a forward end of a first predetermined diameter for extending through said hole in said punch and up to said anvil to form the central hole in a core, and having an elongated second portion of a second predetermined diameter which is greater than said first diameter; said hole in said punch having a forward portion of a diameter approximately equal to said first predetermined diameter of said forward core rod end to form a close sliding fit therewith, and said hole in said punch having a rearward portion which is of a diameter sufficiently greater than said second predetermined diameter of said second core rod portion to provide a clearance of at least five times the clearance around said forward core rod portion, to substantially prevent sliding contact between the punch and core rod therealong; means for holding said core rod stationary with its extreme forward end approximately even with said anvil; and means for reciprocating said punch toward and away from said anvil.
 3. Apparatus for pressing magnetic cores comprising: a die of hard material having a central hole for receiving magnetic core material; an anvil movable over said die; means for reciprocating a punch along said die; means for holding a core rod in extension through a hole in a punch that is being reciprocated and in extension through said die up to said anvil; a punch of hard material having a hole extending therethrough, said punch hole having a forward hole portion of a first diameter and a rearward hole portion of a second diameter greater than said first diameter, the outside of said punch having a forward part with a diameter approximately equal to the diameter of said die hole and a rearward part of a greater diameter; and a core rod extending completely through said punch hole, and including a pin of hard material of a constant diameter substantially equal to said first diameter of said punch hole and an elongated support of a material less hard and less brittle than the material of said pin, said support having a central hole of a diameter approximately equal to the diameter of said pin and said pin extending through said support hole and fastened to said support, said support having a forward part of a diameter sufficiently less than said second diameter of said punch hole to provide a clearance of at least five times the clearance around said forward core rod portion, to prevent contact with the walls of said punch hole in normal operation.
 4. The apparatus described in claim 3 wherein: the difference between said second diameter of said punch hole and said forward part of said support of said core rod is more than ten times as great as the difference between said first diameter of said punch hole and the diameter of said pin of said core rod. 